In the manufacture of pulp and paper wood is usually chipped into particles generally known as chips via equipment known in the trade as a chipper. Many different types of chippers are available, however, the conventional chipper cuts across the wood at an angle to the grain to define the length of the chip, the thickness being determined by splitting along the grain and therefore despite the fact that much work has been done on designing the cutting angles etc. the thickness of the chips is not accurately controlled.
It is also known to cut with a plurality of discrete blades each extending substantially parallel to the grain thereby to produce what is known as wafer chips which are of relatively uniform thickness and have been proven to produce more uniform pulps requiring less cooking chemical for cooking.
However, if benefits are to be derived from the use of wafer chips substantially only wafer chips may be used to charge the digester and since current practice is to purchase chips from many suppliers, it is difficult, if not impossible, to economically purchase only wafer chips. Thus the benefits inherent in wafer chips are not normally available in the pulp mill.
It has also been proposed to screen the chips by thickness and then to slice the oversize chips to reduce the thickness of the chip to a predetermined maximum. One such device for slicing oversize chips is shown for example in U.S. Pat. No. 4,235,382 issued Nov. 25, 1980 to Smith.